A vehicle includes various systems that may operate during an ignition-off condition. For example, a theft deterrent system may be active during the ignition-off condition to detect potential theft and generate a warning signal. Systems that are active during the ignition-off condition draw power from a battery which is not charged during the ignition-off condition. Over time, the active systems can cause the battery state of charge to fall below a threshold at which the battery can no longer provide sufficient power to start the engine. Including more electronic systems that operate during ignition-off conditions further aggravates this problem. An obvious solution might be to increase the power capability of the battery. Such a solution increases the size and weight of the battery and can affect cost, packaging, and fuel economy.